Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Junya Sumita is active.

Publication


Featured researches published by Junya Sumita.


Journal of Nuclear Science and Technology | 2009

Development of an Evaluation Model for the Thermal Annealing Effect on Thermal Conductivity of IG-110 Graphite for High-Temperature Gas-Cooled Reactors

Junya Sumita; Taiju Shibata; Shigeaki Nakagawa; Tatsuo Iyoku; Kazuhiro Sawa

The thermal conductivity of graphite components used as in-core components in high-temperature gascooled reactors (HTGRs) is reduced by neutron irradiation during reactor operation. The reduction in thermal conductivity is expected to be reversed by thermal annealing when the irradiated graphite component is heated above its original irradiation temperature. In this study, to develop an evaluation model for the thermal annealing effect on the thermal conductivity of IG-110 graphite for the HTGRs, the thermal annealing effect evaluated quantitatively at irradiation temperatures of up to 1,200°C and neutron fluences of up to 1.5 dpa. Moreover, the thermal conductivity of IG-110 graphite was calculated by using a modified thermal resistance model considering the thermal annealing effect. The following results were obtained. (1) The thermal annealing effect on the thermal conductivity of IG-110 graphite could be evaluated quantitatively and a thermal annealing model was developed based on the experimental results at irradiation temperatures of up to 1,200°C and neutron fluences of up to 1.5 dpa. (2) The thermal conductivities of IG-110 graphite calculated by using the modified thermal resistance model considering the thermal annealing effect showed good agreement with experimental measurements. This study has shown that it is possible to evaluate the annealed thermal conductivity of IG-110 graphite by using the modified thermal resistance model at irradiation temperatures of 550–1150°C and irradiation fluences of up to 1.5 dpa.


International Journal of Nuclear Energy | 2013

A Small-Sized HTGR System Design for Multiple Heat Applications for Developing Countries

Hirofumi Ohashi; Hiroyuki Sato; Minoru Goto; Xing Yan; Junya Sumita; Yujiro Tazawa; Yasunobu Nomoto; Jun Aihara; Yoshitomo Inaba; Yuji Fukaya; Hiroki Noguchi; Yoshiyuki Imai; Yukio Tachibana

Japan Atomic Energy Agency has conducted a conceptual design of a 50 MWt small-sized high temperature gas cooled reactor (HTGR) for multiple heat applications, named HTR50S, with the reactor outlet coolant temperature of 750°C and 900°C. It is first-of-a-kind of the commercial plant or a demonstration plant of a small-sized HTGR system to be deployed in developing countries in the 2020s. The design concept of HTR50S is to satisfy the user requirements for multipurpose heat applications such as the district heating and process heat supply based on the steam turbine system and the demonstration of the power generation by helium gas turbine and the hydrogen production using the water splitting iodine-sulfur process, to upgrade its performance compared to that of HTTR without significant R&D utilizing the knowledge obtained by the HTTR design and operation, and to fulfill the high level of safety by utilizing the inherent features of HTGR and a passive decay heat removal system. The evaluation of technical feasibility shows that all design targets were satisfied by the design of each system and the preliminary safety analysis. This paper describes the conceptual design and the preliminary safety analysis of HTR50S.


Journal of Nuclear Science and Technology | 2010

Investigation of Microstructural Change by X-ray Tomography and Anisotropic Effect on Thermal Property of Thermally Oxidized 2D-C/C Composite for Very High Temperature Reactor

Junya Sumita; Taiju Shibata; Eiji Kunimoto; Masatoshi Yamaji; Takashi Konishi; Kazuhiro Sawa

Two-dimensional carbon fiber reinforced carbon composite (2D-C/C composite) is one of the candidate materials for reactor internals, e.g., control rod element, of Very High Temperature Reactor (VHTR) because of its high strength at high temperature and thermal stability. From the viewpoint of its application to the reactor internals of the VHTR, it is important to investigate the anisotropic effect on its properties for the design and safety analysis of the VHTR. Since the properties of the 2D-C/C composite are strongly dependent on its microstructure, it is necessary to observe its microstructural variations to correlate to the changes in its properties. This study has shown that X-ray tomography can be applied to observe the internal microstructural change of the thermally oxidized 2D-C/C composite. The relationship between the change in properties, including the thermal conductivity, coefficient of thermal expansion (CTE), and burn-off of the thermally oxidized 2D-C/C composite, can be expressed using the empirical exponential decay formula in both directions perpendicular and parallel to the lamina. The direction of the hexagonal graphite crystal structure from the carbon atoms and the microstructure of the 2D-C/C composite can explain not only the relationship between changes in the thermal conductivity, CTE, and burn-off but also the difference in the changes in the thermal conductivity and CTE between fiber directions.


Journal of Nuclear Science and Technology | 2014

Investigation on structural integrity of graphite component during high temperature 950 °C continuous operation of HTTR

Junya Sumita; Yosuke Shimazaki; Taiju Shibata

Graphite material is used for internal structures in high temperature gas-cooled reactor. The core components and graphite core support structures are so designed as to maintain the structural integrity to keep core cooling capability. To confirm that the core components and graphite core support structures satisfy the design requirements, the temperatures of the reactor internals are measured during the reactor operation. Surveillance test of graphite specimens and in-service inspection using TV camera are planned in conjunction with the refueling. This paper describes the evaluation results of the integrity of the core components and graphite core support structures during the high temperature 950 °C continuous operation, a high temperature continuous operation with reactor outlet temperature of 950 °C for 50 days, in high temperature engineering test reactor. The design requirements of the core components and graphite core support structures were satisfied during the high temperature 950 °C continuous operation. The dimensional change of graphite which directly influences the temperature of coolant was estimated considering the temperature profiles of fuel block. The magnitude of irradiation-induced dimensional change considering temperature profiles was about 1.2 times larger than that under constant irradiation temperature of 1000 °C. In addition, the programs of surveillance test and ISI using TV camera were introduced.


IOP Conference Series: Materials Science and Engineering | 2011

Study on Fracture Behavior of 2D-C/C Composite for Application to Control Rod of Very High Temperature Reactor

Junya Sumita; I Fujita; Taiju Shibata; T Makita; T Takagi; E Kunimoto; Kazuhiro Sawa; W Kim; J Park

For a control rod element of the Very High Temperature Reactor, a carbon fiber reinforced carbon matrix composite (C/C composite) is one of the major candidate materials for its high strength and thermal stability. In this study, in order to establish the data base of the 2D-C/C composite, the fracture data was obtained by simulating the crack expected to be generated under the VHTR condition and the oxidation effect on the fracture behavior was evaluated. Moreover, the fracture mechanism of the C/C composite was investigated through scanning electron microscope observation. This study showed that the oxidized matrix caused reduction of the fracture toughness and the reduction ratio was dependent on the density of matrix and a number cracks. With increasing the oxidation, the fracture toughness is mainly dependent on the fiber characteristics. Furthermore, the crack grows along the boundary between fiber bundles without breaking the fiber. The cracks which were initiated at the interface between the matrix and the fiber were gathered into the voids in the boundary between fiber bundles, and, then, the cracks grew up in the matrix.


IOP Conference Series: Materials Science and Engineering | 2011

Research and developments on application of carbon-carbon composite to HTGR/VHTR in Japan

M Eto; T Konishi; Taiju Shibata; Junya Sumita

High Temperature Gas-cooled Reactor (HTGR) and Very High Temperature Reactor (VHTR) are attractive nuclear reactors to obtain high temperature helium gas at the reactor outlet. To enhance the thermal efficiency, the in-core internals of HTGR/VHTR, especially control rods, are subjected to the severe thermo-mechanical condition. The carbon-carbon (C/C) composite is one of the advanced material candidates for the control rod sheath of the advanced reactors where the excellent thermal resistance and stability are required because of the possible severe condition. The Research and development on the C/C composite application to HTGR have been carried out since 1990s. JAEA and Toyo Tanso have carried out the R & D on C/C composite to be used for control rod. Application of C/C composite is recently focused as one of the important subjects to develop VHTR in the international R & D activities. Scheme of the development in the JAEA/Toyo collaboration is outlined as follow: After the feasibility of C/C composite rod was demonstrated by a conceptual design, the procedure is progressing as follows; (1) Database establishment, (2) Design and manufacturing of components, and (3) Demonstration test by High Temperature engineering Test Reactor.


IOP Conference Series: Materials Science and Engineering | 2011

Correlation of Microstructure and Compressive Strength of C/C Composite Using X-ray Tomography

Junya Sumita; Taiju Shibata; Eiji Kunimoto; Masatoshi Yamaji; Takashi Konishi; Kazuhiro Sawa

For the control rod element of a Very High Temperature Reactor, carbon fiber reinforced carbon matrix composite (C/C composite) is one of the major candidate materials for its high strength and thermal stability. In this study, in order to correlate the microstructure of the C/C composite to its compressive strength, the X-ray tomography was applied to visualize the internal microstructure of the C/C composite. The relationship between change in the compressive strength and that in the microstructure was also investigated. This study showed that the pore distribution in the C/C composite could be confirmed visually and the volume and shape of the pores could be evaluated by the X-ray tomography in three-dimension. Moreover, since the matrix was gradually lost and transverse cracks became large with increasing the oxidation, the bonding strength between fiber bundles became weak and the compressive strength of parallel to lamina decreased.


Journal of Nuclear Materials | 2008

Non-destructive evaluation methods for degradation of IG-110 and IG-430 graphite

Taiju Shibata; Junya Sumita; Tatsuya Tada; Satoshi Hanawa; Kazuhiro Sawa; Tatsuo Iyoku


Journal of Solid Mechanics and Materials Engineering | 2008

Oxidation Damage Evaluation by Non-Destructive Method for Graphite Components in High Temperature Gas-Cooled Reactor

Taiju Shibata; Tatsuya Tada; Junya Sumita; Kazuhiro Sawa


Nuclear Engineering and Design | 2014

R&D plan for development of oxidation-resistant graphite and investigation of oxidation behavior of SiC coated fuel particle to enhance safety of HTGR

Shohei Ueta; Junya Sumita; Taiju Shibata; Jun Aihara; Ichiro Fujita; Jun Ohashi; Yoshihide Nagaishi; Takenori Muto; Kazuhiro Sawa; Nariaki Sakaba

Collaboration


Dive into the Junya Sumita's collaboration.

Top Co-Authors

Avatar

Taiju Shibata

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Kazuhiro Sawa

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Eiji Kunimoto

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Hiroyuki Sato

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Xing L. Yan

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Yukio Tachibana

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Atsuhiko Terada

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Masatoshi Yamaji

Japan Atomic Energy Research Institute

View shared research outputs
Top Co-Authors

Avatar

Tatsuya Tada

Japan Atomic Energy Agency

View shared research outputs
Top Co-Authors

Avatar

Yasunobu Nomoto

Japan Atomic Energy Agency

View shared research outputs
Researchain Logo
Decentralizing Knowledge